The present invention relates in general to dual fluid atomizers, and in particular to internal mix atomizers having new and improved nozzle designs.
Dual fluid atomization is a method which uses the momentum supplied by a compressible fluid (usually air or steam) to break a liquid up into very fine droplets. For the case described here, this is done by internally mixing the liquid and compressible fluid and spraying the mixture into the surrounding gas through small orifices. These orifices are typically sharp edged at both their inlet and their outlet.
Often, processes which utilize dual fluid atomizers involve spraying into a dusty environment and have problems with deposition around the outlet of the atomizer orifices. Among current methods of dealing with these problems are physically cleaning the atomizers in situ, shutting down the process to physically clean the atomizers, or using vent air (i.e. a clean air flow around the immediate vicinity of the atomizers) to reduce the deposition of dust on the atomizers.
A few nozzle designs are known which incorporate a single discharge hole with a conical outlet. (See, for example, U.S. Pat. No. 4,625,916 and J.M. Beer & N.H. Chigier, Combustion Aerodynamics, Robert E. Krieger Publishing Company, Malabar, Fl., 1983 (pp. 124-127 & p. 187). There is no suggestion to shape the nozzle to maintain spray quality (i.e. drop sizes) at constant consumption and pressure of a compressible fluid or for the purpose of controlling atomizer deposition, in these references, however.
U.S. Pat. No. 3,419,220 depicts a tapered nozzle on the entrance side to make the nozzle more wear-resistant. U.S. Pat. No. 4,625,916 provides a nozzle having a bore which diverges on the exit side. There is nothing in either of these two references which suggests a combination of these features or suggests a resulting reduction in deposition or a decrease in irrecoverable pressure losses. Other references of interest are G. M. Blythe, et al, Evaluation of a 2.5-MW Spray Dryer/Fabric Filter SO.sub.2 Removal System, EPRI Report #CS-3953, May, 1985 (pp. 9-10); and M. Babu, et al, Duct Injection Technologies for SO.sub.2 Control, First Combined FGD and Dry SO.sub.2 Control Symposium, Paper No. 10-2, Oct., 1988 (p. 73).